1. Field of Invention
The present invention relates to a bandgap circuit, more particularly to an adjusting circuit for adjusting a reference voltage outputted from the bandgap circuit.
2. Description of the Related Art
The trend of the semiconductor industry nowadays is heading towards design so that the integration of 3C (consumer, computer and communication products) and systems on chips (SOC) are most desirable. The purpose is to reduce the cost, increase efficiency and reduce power consumption, and also to develop lighter, thinner, shorter and smaller portable electronic devices, which may be possible by adopting a more precise design technology and a better process. The present chip unit can carry several chips, and integration of various elements is at a remarkable progress.
The chips on the circuit need a reference voltage generating circuit for generating a reference voltage; for example, the reference voltage is set based on the expectation of excellent temperature stability and a stable voltage supply. In other words, the setting of the reference voltage is required to be apart from external environment. However, the reference voltage generating circuit may result in voltage deviation due to different semiconductor process conditions. Therefore, for solving the issue of deviation, some manufacturers propose using a plurality of small resistors connected to a main resistor of the reference voltage generating circuit. Referring to FIGS. 1 and 2, a fine adjusting circuit B is connected to a main resistor A1 of the reference voltage generating circuit A, namely bandgap circuit. The fine adjusting circuit B comprises a plurality of resistors B1 connected to the main resistor A1 in series, and the resistors B1 are respectively connected to fuses B2 in parallel. Thus, the resistors B1 can fine adjust the value of the main resistor A1 according to the status of the fuses B2 connected to the resistors B1.
The above conventional reference voltage generating circuit A (bandgap circuit) has the following defects.
1. The conventional reference voltage generating circuit A can only burn out the fuses B2 but not add the fuses B2 after the chips are formed. Therefore, for fine adjusting the positive and the negative terminals, the fuses B2 should not be blown out before the chips are processed. Accordingly, an output voltage A2 (VBG) of the reference voltage generating circuit A is low, as shown in FIG. 2.
2. The conventional fuses B2 are blown out by the current, and when the current is controlled inappropriately, the reference voltage generating circuit A may get damaged.
3. In the above fine adjusting circuit B, the fuses B2 must be blown out in order to obtain a “0” or “1” signal. Therefore, the chips must be processed before packaged, or otherwise the “0” or “1” setup cannot precisely meet the requirement.
Therefore, how to overcome the conventional defects described above is an important issue for manufacturers in the field.